a) Field of the Invention
This invention relates to dental compositions. More particularly, it relates to dental compositions which comprise conventional dental compositions having incorporated therein a polymer (grafted rubber) obtained by polymerizing at least one ethylenically unsaturated monomer in the presence of a rubber and which can yield cured products having excellent strength properties.
b) Description of the Prior Art
In the field of dental materials, conversion from metallic materials to polymeric materials is proceeding rapidly in recent years. Such dental materials include, for example, surface coating agents such as surface glazing agents and hard coating agents; composite resins such as filling composite resins, facing hard resins, composite resin inlays and jacket crowns; artificial teeth, denture bases and denture base liners; and orthodontic materials such as special impression tray materials and brackets.
Usually, these dental materials are composed chiefly of a (meth)acrylic ester compound and a polymerization initiator. Moreover, if need arises from the intended purpose, they can additionally contain inorganic materials, (meth)acrylic ester polymers, pigments, solvents, polymerization inhibitors, oxidation stabilizers and the like. Typically, they are cured by photopolymerization by means of visible light or ultraviolet radiation, by thermal polymerization, or by redox polymerization. Such cures are often performed in the mouth.
When such polymeric materials are regarded as dental substitute materials, they are more excellent in adhesion, appearance and workability than metallic materials. However, their mechanical properties such as strength have been still unsatisfactory.
With particular reference to molar composite resins which are materials for the restoration of molars, great importance is attached to their strength properties, because they are subject to high occlusal pressure characteristic of molars. In order to solve this problem, the concept of composite resin inlays has been proposed recently. This is based on the technique in which, outside the mouth, a composite resin is cured by two-stage polymerization (i.e., photopolymerization and thermal polymerization) to form an inlay having elevated crosslinking density and hence improved strength properties. However, several problems concerning pot life, workability and impact resistance remain to be solved.
Moreover, a composite denture base resin in which a siloxane polymer having a ladder structure is blended with PMMA in molecular order has also been proposed (Dental Materials and Equipment (in Japanese), 6, 4, 529, 1987). However, this is less than satisfactory.
In view of these circumstances, the present inventors made an intensive study and have found that, if a grafted rubber obtained by polymerizing at least one ethylenically unsaturated monomer in the presence of a rubber is incorporated in a conventional dental composition, there can be obtained a novel dental composition capable of yielding a cured product having excellent strength properties. The present invention has been completed on the basis of this finding.